What should have been a simple "10 minute job", has now turned into quite a nightmare!

The driver's side door was making a grinding noise of my '86 560SL, and I located the noise to be coming from the door check strap. After ordering a new check strap, I removed the door panel and extracted the old check strap from inside the door with some difficulty - I could only pull the thing out after removing the springs on the actual strap.

For the life of me, I cannot seem to squeeze the new check strap past the gap formed by the inside panel of the door and the electric window motor into the appropriate place. Do I need to remove the motor or am I just being too delicate?

I have a strange banging sound coming from the driver's door from my 560sl. Strangely, when I open the door while the car is in motion the sound goes away. I was wondering if this noise is coming from a door strap going bad? Any ideas would help.
Thanks
Larry '86 560sl